Fluid flow direction detector

ABSTRACT

An apparatus for detecting the flow direction of a fluid between two enclosed spaces, such as hospital rooms, includes a conduit extending along a horizontal plane and adapted to receive the fluid. A detecting element is disposed within the conduit and movable in the direction of fluid flow, the detecting element being in direct contact with the fluid. A sensing element may be coupled to the conduit for determining when the detecting element reaches a predetermined position within the conduit. The circuitry coupled to the sensing element enables selection of a desired flow direction and actuates an alarm when the detected flow direction is other than the one selected.

This application is a Continuation-In-Part of application Ser. No.07/764,808, filed on Sept. 24, 1991, now issued as U.S. Pat. No.5,291,182, which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to sensing devices, and more particularly, to adevice for detecting the directional flow of air into or out of a roomand its adjoining spaces and in some embodiments for actuating an alarmupon the occurrence of an undesirable flow direction.

BACKGROUND OF THE INVENTION

The direction of air flow into or out of a room depends on the pressureof the room relative to its adjacent spaces. The differential pressurebetween the room and the adjacent spaces need only be slight,practically immeasurable, to create air flow. Rooms such as hospitaloperating rooms, patient isolation rooms, sterilization rooms, researchlaboratories, clean rooms, etc., often require directional air flow. Forexample, a patient isolation room, containing a patient who issusceptible to infection, is supplied with highly filtered air underpositive pressure, i.e., clean air flows out of the room at all times,thereby preventing dirty or infectious air from entering the room. Thisis accomplished by supplying clean air to the patient's room at agreater flow rate than the rate at which air is exhausted from the room.Conversely, if the patient is infectious or the room contains toxins,the room should be kept under negative pressure, i.e., the rate at whichpotentially contaminated air is exhausted from the room is greater thanthe rate at which new air is supplied to the room.

In the above described environments, it is important that the properdirection of air flow be maintained. If the proper direction or air flowceases, a detecting element should indicate the improper situation. Insome instances, an alarm may be activated until the pressure conditionin the room can be corrected.

Transducers are currently available that measure the differentialpressure between a room and reference space and use of the resultingmeasurement for alarm actuation. A problem associated with these typesof differential pressure sensors is that the room must be well sealed or"tight" in order to build up a measurable pressure. When a door orwindow is open for an appreciable period of time, the differentialpressure of the room approaches zero causing the sensor to falselyactuate the alarm, despite the presence of directional air flow into orout of the room. Accordingly, there is a need for a device which candetect the directional air flow into or out of a room without relying ondifferential pressure measurements.

Another type of transducer currently available utilizes a "hot wire"anemometer to detect the directional velocity of air. Such transducersare an improvement over a differential pressure transducer. However,their accuracy is dependent upon the sensitivity and proper calibrationof the transduction element and the associated processing circuitry.

Further, since neither air pressure nor air velocity can be seen, peopleoften hang a piece of string or tissue in a doorway or in front of avent to assess the direction of air flow into or out of a room and toverify the results of either differential pressure or anenometer-typetransducer.

U.S. Pat. Nos. 2,808,580, Fuller; 3,192,470, Wadey; 3,689,908, Ray;3,820,396, Gamer et al.; 4,486,744, Pratt et al.; 4,774,676, Stenzel etal.; and 4,963,857, Sackett; all disclose devices for detecting thepresence and velocity of a fluid, typically a gas. However, none ofthese references disclose a device which allows the desired flowdirection of a fluid to be selected and which actuates an alarm when thedetected direction is other than the desired direction.

Accordingly, there exists a need for a device which allows the desireddirection of air flow to be selected and visually monitored, and/or,which actuates an alarm when the detected direction is other than theone selected.

It is therefore an object of this invention to provide a device fordetecting the presence and direction of air flow between two rooms or aroom and its adjoining spaces.

Another object of the present invention is to provide a device whichallows the desired direction of air flow to be selected.

A further object of the present invention is to provide a device whichindicates when the detected direction of air flow is different from theselected direction of air flow.

Still another object of the present invention is to provide a device fordetecting the presence and direction of air flow between a room and itsadjoining spaces which does not require that the room be well sealed,i.e., at near zero differential pressure.

A further object of the present invention is to provide a device fordetecting the presence and direction of air flow whose accuracy does notdepend primarily on the sensitivity and calibration of the transducerand associated processing circuitry.

Yet another object of the present invention is to provide a device fordetecting presence and direction of air flow which allows for directvisual confirmation of the direction of air flow.

BRIEF SUMMARY OF THE INVENTION

The foregoing and other objects of the present invention are achievedwith an apparatus for detecting the flow direction of a fluid comprisinga conduit adapted to receive the fluid. A detecting element is disposedwithin the conduit and is movable in the direction of fluid flow. Asensing element may be coupled to the conduit to determine when thedetecting element reaches a predetermined position within the conduit.

In one embodiment of the present invention, the conduit comprises acylindrical tube extending along a horizontal plane. The moving elementcomprises a lightweight sphere disposed within the tube and translatablein the direction of fluid flow. In this embodiment, the sensing elementcomprises a pair of optical sensors disposed at opposite ends on thetube and within the path of the sphere.

In another embodiment, the conduit comprises a rectangularly shaped tubehaving a rectangular bore. The moving element comprises a flap pivotallycoupled to the rectangular bore and deflectable in the direction offluid flow. In this embodiment, the sensing element comprises a pair ofoptical sensors symmetrically positioned about the flap whenundeflected.

In still another embodiment a circuit, coupled to the sensing element,indicates the direction of fluid flow through the conduit. The circuitincludes elements for selecting the desired direction of the fluid flowand means for indicating when the detected flow direction is other thanthe one selected and for actuating an alarm when the detected directionis other than the one selected.

In another series of embodiments of the present invention, a singlesphere or pair of spheres may be used to provide a visual indication ofthe direction of the fluid flow. Moreover, the tube along which thesphere or spheres move may be straight, concave, or disposed at an anglerelative to the wall.

In still another embodiment, the conduit may have small inlet/outletopenings to mitigate or eliminate harmful fluids from flowing throughthe system in an undesired direction.

The invention will be more fully understood from the detaileddescription set forth below, which should be read in conjunction withthe accompanying drawings. The invention is defined in the claimsappended at the end of the detailed description, which is offered by wayof example only.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a side cut-away view of an air flow detector in accordancewith a first embodiment of the present invention;

FIG. 2 is a cross-sectional view of the air flow detector of FIG. 1 asseen on line 2--2;

FIG. 3 is a front view of the control panel of the air flow detector ofFIG. 1;

FIG. 4 is a perspective view of the air flow detector of FIG. 1;

FIGS. 5A-B are electrical schematics of the circuitry of the air flowdetector in accordance with the present invention;

FIG. 6 is a side cut-away view of an air flow detector in accordancewith a second embodiment of the present invention;

FIG. 7 is a front view of the air flow detector of FIG. 6;

FIG. 8 is a side cut-away view of an alternate embodiment of the airflow detector of FIG. 6;

FIG. 9 is a front view of the air flow detector apparatus of FIG. 8;

FIG. 10 is a perspective view of embodiments of the present inventionsecured within a wall;

FIG. 11 is a side view of the two-sphere version of FIG. 10;

FIG. 12 is a side view of another embodiment of the present invention;

FIG. 13 is a side view of the two-sphere version of FIG. 12;

FIG. 14 is a side view of another embodiment of the present invention;

FIG. 15 is a side view of the two-sphere version of FIG. 14;

FIG. 16 is a side view of another embodiment of the present invention,;

FIG. 17 is a side view of the two-sphere version of FIG. 16; and

FIG. 18 is a perspective end view taken along the line 18--18 of FIG.16.

DETAILED DESCRIPTION

Referring now to the drawings, particularly FIGS. 1-5B, there is shownan air flow direction detector 10 in accordance with a first embodimentof the present invention. In the illustrative embodiment, detector 10extends transversely through a wall 12 or similar structure separatingtwo rooms, such as hospital rooms, or a room and its adjoiningenclosures. A room is considered to be any substantially enclosed space,although not necessarily a sealed or "tight" space. Detector 10comprises housing sections 14A-B, tube 16, sphere 20, sensors 22 and 24,stop pins 26, control panel 78 and electrical circuits 30 and 60.

In the first embodiment of the present invention, tube 16 is an elongatecylinder having open ends 16A-B, as shown in FIG. 1. Tube 16 may have alength of approximately 8 inches. A bore 18 extends through tube 16.Bore 18 has a uniform diameter of approximately 1 1/2 inches and asmooth surface to minimize the resistance between itself and sphere 20,as explained hereinafter. Tube 16 is formed from a rigid material,typically plastic, and may be transparent, translucent or opaque. Tube16 extends through wall 12 along a horizontal level plane to avoidbiasing the motion of sphere 20 in either direction as it moves throughbore 18. A pair of stop pins 26 extend through apertures in the wall oftube 16 and across the diameter of bore 18. Stop pins 26 prevent sphere20 from exiting open ends 16A-B of tube 16 while still allowingunrestricted air flow through bore 18 diameter.

Sphere 20 is disposed in bore 18 of tube 16, as shown in FIGS. 1-4.Sphere 20 may be formed of a lightweight material, such as plastic, andmay have a hollow interior, similar to a ping-pong ball. The exteriorsurface of sphere 20 is smooth to minimize friction between itself andbore 18, allowing the sphere to traverse bore 18 in the presence ofminimal air flow. The diameter of sphere 20 is approximately 80% of thediameter of bore 18.

Sensors 22 and 24 extend through the wall of tube 16 and are exposed tothe interior of bore 18. The end surfaces of sensors 22 and 24 are flushwith the surface of bore 18 to prevent interference with the motion ofsphere 20 through the bore. Sensor 22 is located outside the room beingcontrolled for proper pressurization and sensor 24 is located inside theroom. Sensors 22 and 24 are coupled to circuits 30 and 60 and detect thepresence of sphere 20, as explained hereinafter.

Referring to FIGS. 1 and 4, end 16A of tube 16 projects from wall 12into the room or enclosure in which the pressure is to be monitored. Asubstantially rectangular housing section 14A, shown transparent forpurposes of viewing the position of sphere 20, surrounds end 16A andcontains one or more apertures 15A which provide fluid communicationbetween the room interior and tube 16. Housing section 14B, similar inconstruction to section 14A, surrounds end 16B of tube 16 where itprotrudes from the opposite side of wall 12, as illustrated in FIG. 1.Control panel 78 is integrated to the front surface of housing section14B to allow for visually monitoring the position of sphere 20 directly,the position of sphere 20 via LED 52 and LED 58, the status of an alarmcondition and for changing the desired direction of air flow via switch66. Control panel 78 can be located inside or outside the room beingmonitored. The room being monitored preferably has active supply andexhaust vents, i.e., fans are present in both vents.

Referring to FIGS. 5A-B, the electrical circuits of air flow detector 10are illustrated. Circuit 30 of FIG. 5A is a direct current circuit andincludes a power supply 32 for converting a standard 120 volt AC lineinput into a 24 volt DC output. The positive terminal of power supply 32is connected to the contact of a single-pole, double-throw (SPDT) switch40 through a fuse 34. A first terminal of switch 40 is connected to aterminal of Light Emitting Diode (LED) 38, which may be a blinking-typeLED. The other terminal of LED 38 is connected to the negative terminalof power supply 32 through a resistor 36. A second terminal of switch40, hereinafter referred to as node 45, is connected to a first terminalof relay contact 42 of time delay relay coil 70 of circuit 60, asexplained hereinafter. Relay contact 42 is normally in a closed positionwhen relay coil 70 is not energized. A piezoelectric horn 44 and a lightemitting diode 46 are connected in parallel between the second terminalof relay contact 42 and the negative terminal of power supply 32,hereinafter referred to as node 35. LED 46 may be red in color toindicate an alarm condition.

Sensors 22 and 24 are implemented, in the illustrative embodiment, withphotoelectric diffuse sensors. Each of the photoelectric diffuse sensorsincludes an emitter and a receiver element in the same housing. Theemitter sends out a beam of pulsed, infrared light which is reflecteddirectly by sphere 20. When the beam hits the surface of sphere 20, itis diffused or scattered in all directions, with some of the light beingreflected back to the receiver element of the sensor. The operatingrange of sensors 22 and 24 is dependent largely on the reflectiveproperties of the surface of sphere 20. Each of the sensors includes afiber optic cable adapter which is mounted through the wall of tube 16and exposed to the interior of bore 18, as illustrated in FIGS. 1-2 and4. A photoelectric diffuse sensor suitable for use as sensors 22 and 24in the present invention is Model No. FZAN 18N 1005 commerciallyavailable from Baumer Electric, Southington, Conn. 06489.

Sensors 22 and 24 are three-terminal devices, illustrated in FIG. 5A. Afirst terminal of sensor 22 is connected to node 45 while a secondterminal thereof is connected to node 35. An LED 52 and first relay coil54 are connected in parallel between node 45 and the third terminal ofsensor 22. In the illustrative embodiment, LED 52 is green forindicating positive pressure, i.e., directional airflow is out of thesubject room. Sensor 24 similarly has a first terminal connected to node45 and a second terminal connected to node 35. An LED 58 and secondrelay coil 55 are connected in parallel between node 45 and the thirdterminal of sensor 24. In the illustrative embodiment, LED 58 is yellowfor indicating negative pressure, i.e., directional airflow is into thesubject room. DC circuit 30 is electrically isolated from AC circuit 60but is mechanically coupled therewith by relay contacts 42, 64 and 65,as explained hereinafter.

As shown in FIG. 5B, AC circuit 60 includes a transformer 62 whichtransforms a 120 volt AC line voltage to 24 volts AC. One terminal oftransformer 62, hereinafter referred to as node 77, is connected to afirst terminal of each of contacts 66A-D of two-position rotary switch66. Switch 66 is a double-pole, double-throw (DPDT) switch in whichcontacts 66A and 66D are closed when the switch is in the positiveposition, as illustrated in FIG. 5B. Contacts 66B-C are closed whenswitch 66 is in the negative position. The second terminal of contact66A of switch 66 is connected to a first terminal of relay contact 64 ofrelay coil 54. The second terminal of contact 64 is connected to a firstterminal of time delay relay coil 70. The second terminal of relay coil70 is connected to a second terminal of transformer 62, hereinafterreferred to a node 75. The second terminal of contact 66B of switch 66is connected to a first terminal of relay contact 65 of second relaycoil 55. The second terminal of relay contact 65 is connected to thefirst terminal time delay relay coil 70. As shown in FIG. 5B, relaycontacts 64 and 65 are normally in an open position when relays 54 and55 are not energized, respectively.

A second terminal of contact 66C is connected to a terminal of first(open) winding 72A of an exhaust damper motor (not shown) which is usedto open or close a damper over an active exhaust vent of the room beingmonitored. A second terminal of the motor winding 72A is connected tonode 75. The second terminal of contact 66D of switch 66 is connected toa terminal of a second (close) winding 72B of the exhaust damper motor.A second terminal of winding 72B is connected to node 75.

Control panel 78 of air flow detector 10 is illustrated in FIG. 3.Switches 40 and 66, LEDs 30, 46, 52 and 58, and alarm 44 are mounted oncontrol panel 78 to select and indicate the selected mode and status ofdetector 10, as explained hereinafter. Some of the elements of circuits30 and 60 may be mounted on a circuit board disposed behind controlpanel 78 which is formed integrally within the front surface of housingsection 14B. Others, particularly power supply 32, transformer 62, andrelays 54 and 55, may be located in a separate housing which is locatedremotely from detector 10 but which is electrically coupled to controlpanel 78.

The operation of detector 10 occurs as follows. The following initialpowering of the circuits 30 and 60, the position of switch 66 is set toselect the desired pressure conditions, i.e., the direction of air flowinto or out of the room of concern. For the purposes of illustration,switch 66 is set to the positive position, as indicated in FIG. 5B,indicating that the room is to be under positive pressure. In this mode,the desired direction of air flow is out of the room. Assuming that theroom is currently under positive pressure, air will enter housingsection 14A and flow through bore 18 of tube 16. The flow of air throughbore 18 will overcome any rolling friction between sphere 20 and bore 18and translate sphere 20 in the direction of sensor 22. Stop pin 26 willprevent sphere 20 from exiting tube end 16B and will retain sphere 20 inthe proximity of sensor

Referring to FIG. 5A, in the positive mode, the contact of switch 40 isconnected to node 45 which supplies current to sensor 22, LED 52 andrelay coil 54. Light irradiated from the emitter element in sensor 22 ispartially reflected off the surface of the sphere 20 and into thereceiver element of sensor 22, activating the sensor. Upon activation ofsensor 22, LED 52 and first relay coil 54 are operatively coupled tonode 35. Current flows through LED 52 illuminating the LED andindicating that the room is under positive pressure. Current also flowsthrough first relay coil 54, energizing the coil. Upon energization offirst relay coil 54, contact 64 of circuit 60, which is normally open,closes. Time delay coil 70 is then coupled to node 77 via contact 66Aand contact 64, causing coil 70 to be energized. Upon energization ofcoil 70, contact 42 of circuit 30, which is normally closed, opens,thereby preventing horn 44 and LED 46 from being activated as long assphere 20 is positioned at sensor 22.

As shown in FIG. 5B, winding 72B of the exhaust damper motor is coupledto node 75 and to node 77 by contact 66D when switch 66 is in thepositive position. Winding 72B remains energized, as long as switch 66is in the positive position, and causes the exhaust damper motor toremain closed, regardless of the position of sphere 20 within tube 16.In this manner, the fan in the exhaust vent will not actively draw airfrom the room. Thus, the supply air must exfiltrate the room.

If the direction of air flow through tube 16 reverses, i.e., the roombecomes negative pressurized while switch 66 is still set to a positivemode, the following occurs. The flow of air through bore 18 causessphere 20 to move away from sensor 22 and toward sensor 24. As sphere 20leaves the proximity of sensor 22, the sensor becomes deactivated,effectively stopping the flow of current through LED 52 and relay 54,causing LED 52 to turn off and contact 64 to open via deenergizing relay54. Sphere 20 may continue to move through bore 18 until it is stoppedby pin 26 near sensor 24 at end 16A of tube 16. In such case, sensor 24is then activated, operatively coupling LED 58 and second relay coil 55to node 35. Current flows through LED 58 from node 45 to node 35illuminating the LED and indicating the room is under negative pressure.Current also flows from node 45 to node 35 through second relay coil 55energizing the coil. Upon energization of second relay coil 55, contact65 of circuit 60, which is normally open, closes. Time delay coil 70 isthen coupled to contact 66B of switch 60. However, since contact 66B isnormally open when switch 66 is in the positive position, coil 70 is notconnected to node 77. Hence, the coil 70 will not energize and contact42 of circuit 30 will remain closed, operatively coupling horn 44 andLED 46 to node 45, causing activation thereof. Horn 44 will sound analarm and LED 46 will illuminate red indicating that the direction ofair flow is other than the one selected, i.e., positive pressure. Alarm44 and LED 46 will be activated whenever sphere 20 leaves the proximityof sensor 22, when switch 66 is in the positive position, regardless ofwhether sphere 20 is positioned over sensor 24 or is disposedintermediate sensors 22 and 24.

Brief changes in the position of sphere 20, i.e., minor fluctuations inroom pressure, such as caused by opening or closing a door, areprevented from activating piezoelectric horn 44 and LED 46 by time delayrelay coil 70 which requires a threshold period before energizing andactivating such elements.

When the contact switch 40 is connected to LED 38, sensors 22 and 24 aredeactivated, thereby preventing horn 44 and LED 46 from becoming active.In this configuration, current flows through LED 38 causing the LED tobe illuminated, indicating that the alarm circuit 30 is essentiallydeactivated or "silenced".

From the above explanation, the theory of operation of detector 10 maybe deduced for the situation in which switch 66 is positioned to selectnegative pressurization, i.e., the preferred direction of air flow isinto the room. In this situation, horn 44 and LED 46 will be activated,indicating an alarm condition, whenever sphere 20 leaves the proximityof sensor 24. Also, when switch 66 is set to the negative position, openwinding 72.A of the exhaust damper motor will be activated, regardlessof the position of sphere 20, thereby causing the fan in the exhaustvent to actively draw out more air than the air being supplied to theroom by the supply vent. As a result, makeup air from outside of theroom flows directionally into the room.

It will be obvious to those skilled in the art that sensors 22 and 24may be implemented with other than photoelectric diffuse sensors. Forinstance, sensors 22 and 24 may be implemented with photoelectricreflective sensors or proximity sensors which are magnetically activatedby the presence of a metal covered sphere. It will also be obvious thatcircuit 60 may be configured to control devices other than the exhaustdamper motor of the illustrative embodiment.

Referring to FIGS. 6 and 7, an air flow direction detector 80, inaccordance with a second embodiment of the present invention, compriseshousing section 84A-B, conduit 86, sensors 92 and 94, stop pins 96 andcircuits 30 and 60. Circuits 30 and 60 are identical to that of thefirst embodiment, except that sensors 22 and 24 are designed as sensors92 and 94, respectively. Housing sections 84A-B are similar in shape andstructure to housing sections 14A-B of detector 10, except for changesin dimension to accommodate conduit 86.

In the second embodiment, conduit 86 has a rectangular shape and mayhave a length of approximately 8 inches. A rectangular bore 88 extendsthrough conduit 86 and may have a height of approximately 2 inches and awidth of approximately 3 inches. Conduit 86 may be formed from amaterial similar to that of tube 16 of detector 10. A rectangular flap95, formed from a thin, lightweight material, is movably coupled tobottom surface of bore 88 by a pair of downwardly extending legs, eachof which is coupled to a spiral spring 97, as shown in FIGS. 6 and 7.Spiral springs 97 allow flap 95 to pivot freely in either directionthrough bore 88, without bias. A disc-shaped target 98 is secured to aside edge of flap 95. A pair of stop pins 96 project downwardly from theupper interior surface of the bore 88 and limit the total possible rangeof displacement of flap 95 to an approximately 30° arc.

Sensors 92 and 94 are mounted to an interior side surface of rectangularbore 88. Sensors 92 and 94 are positioned symmetrically about flap 95 inits upright, undeflected, position. When flap 95 is at its maximumdeflection in either direction, and in contact with one of stop pins 96,target 98 covers and activates one of sensors 92 or 94, depending on thedirection of air flow. In this manner, flap 95 and target 98 perform thesame function as sphere 20 of detector 10.

The operation of air flow direction detector 80 is similar to that ofdetector 10. Air flows through bore 88, causing a deflection of flap 95in the direction of air-flow. When flap 95 reaches its maximum extent oftravel, target 98 covers one of sensors 92 and 94 thereby activatingthat sensor. The interaction of sensors 92 and 94 with circuits 30 and60 is identical to that previously explained with regard to sensors 22and 24 of the first embodiment.

Referring to FIGS. 8 and 9, an alternate embodiment of detector 80 isillustrated. In this alternative embodiment, flap 95 is pivotallycoupled to the upper interior surface of bore 88 by a pair of supports100. Sensors 92 and 94 are positioned lower on the interior side surfaceof bore 88 so as to similarly coact with flap 95 and target 98 as in theembodiment illustrated in FIGS. 6-7. Also, stop pins 96 project upwardlyfrom the bottom surface of bore 88.

It may be appreciated from the foregoing explanation, that theillustrative embodiments of the present invention provide a device whichallows the desired direction of air flow to be selected and visuallymonitored and which actuates an alarm, or similar device when the airflow direction detected by the device is other than the one selected.

Other embodiments of the present invention may be seen in FIGS. 10-18.Each of these embodiments is designed to permit visual monitoring of thedetecting element. However, an alarm system of the type described abovemay also be used in conjunction with the embodiment.

FIG. 10 illustrates the basic embodiment comprising a sphere ordetecting element 100 having a diameter slightly smaller than the innerdiameter of the bore or conduit 102 in which it travels. At either endof the conduit 102, are the inlet/outlet openings 104 through whichfluid passes in or out of the monitored area. Each inlet/outlet opening104 may have an optional tamper-proof cover 106, having an opening 107,for protecting the device from damage or vandalism. Each cover 106 ismade of durable hard plastic which is transparent to provide viewing ofthe inlet/outlet openings 104. Stop pins 110 proximal to either opening104 limit movement of element 100 and retain it in the conduit.

The embodiment of FIG. 10 is a one sphere system. It may be convertedinto a two sphere system as shown in FIG. 11. A second sphere 100 isplaced within the conduit 102 and the two spheres 100 are separated by aintermediate pin 112. The intermediate pin 112 is preferably positionedhalf-way along the length of the conduit 102 and extends across theinner diameter of the conduit 102. The intermediate pin 112 ispreferably coplanar with the stop pins 110.

In the two sphere system, each sphere 100 may be marked according to theintended use of the system. For example, one sphere may have an indiciasignifying "good" (such as the word "good" or painted green), and theother sphere may have a "bad" indicia (such as "bad" or painted red orblack). A two sphere system may be desirable to eliminate confusion asto the significance of a sphere locating at a particular opening 104.Also, such a system may be desired when personnel monitoring the systemare frequently changed or even if there is a change in the type ofenvironment being monitored. In some situations, it may be desired thatthe fluid flow from the room, while in other situations the opposite maybe true. By interchanging the spheres, the same conduit 102 may be usedto monitor different conditions. To accomplish this, the covers 106 andstop pins 110 are removed and the spheres are interchanged. The covers106 may be locked to the conduit 102 to prevent undesired removal.

Another embodiment is illustrated in FIGS. 12 and 13. FIG. 13 is the,two sphere version of FIG. 12. In this embodiment, the bore or conduit114 is concave along its length. The sphere 100, or spheres of the twosphere system of FIG. 13, will rest at the bottom of the curve 116 whenthe direction of the fluid flow is either neutral or negligible. Theamount of curve in the conduit 114 is dependent upon the use of thesystem. However, the system should indicate any fluid flow direction ofsignificance to the monitored environment. Because of the use of concaveconduit the force generated by moving air must be more than minimal tomove the elements 100 to the outer ends. Thus, the system provides meansby which minimum thresholds of air flow is required to effect adetection of movement.

In this embodiment, the adaptation to a two-sphere system is simple. Itsadvantages have been mentioned above with respect to the embodiment ofFIG. 11. In the two sphere system of FIG. 13, however, the spheres willrest on opposite sides of the intermediate pin when the fluid directionis minimal or neutral.

Still another embodiment of the present invention is illustrated inFIGS. 14 and 15. The only difference between this embodiment and theembodiment of FIGS. 10 and 11 is that the conduit 102 of the embodimentof FIGS. 14 and 15 is secured at an angle within the wall 12. The degreeof the angle is dependent on the use of the system similar to thedetermining the desired curve of FIGS. 12 and 13.

The embodiment of FIGS. 14 and 15 is preferably set up such that thesphere is visible only at the higher inlet/outlet openings 104, labeled122, when the desired condition is present. When the ball is located atthe lower opening 104, labeled 124, the fluid is either neutral,minimal, or moving in the undesired direction.

When monitoring a detrimental material, the stop pins 110 of the otherembodiments may be replaced with disk-shaped caps 126 as shown in theembodiment of FIGS. 16-18. Each cap 126 has a fluid inlet/outlet opening128 positioned such that the sphere 100, when located against the cap126, inhibits contaminated fluid from escaping through the conduit 102.The location of the opening 128 through the cap 126 is dependent on thedimensions of the sphere 100 used to monitor the direction of the fluidflow. An end view of the cap 126 is illustrated in FIG. 18.

Many of the features of the embodiments may be combined as desired. Forexample, caps 126 may obviously be used in any of the previouslymentioned embodiments. Also, each embodiment may have the optionaltamper resistant covers and audio alarm in combination with the visualmonitoring. In addition, other obvious variations to the presentinvention are considered part of the scope of the invention. Forexample, the conduit 102, while illustrated as having a circularcross-section, may just as simply have an oval or rectangularcross-section.

Having thus described several embodiments of the present invention,various alterations, modifications and improvements will readily occurto those skilled in the art. Such alterations, modifications andimprovements as are made obvious by this disclosure are intended to bepart of this disclosure though not expressly stated herein, and areintended to be within the spirit and scope of the invention. Forexample, the circuitry disclosed may be readily replaced with MatsushitaMP-PC for the power supply and Matsushita S1X for the time delay relay.Accordingly, the foregoing descriptions are intended to be exemplaryonly and not limiting. The invention is limited only as defined in thefollowing claims and equivalents thereto.

What is claimed is:
 1. An apparatus for detecting the flow direction ofa fluid comprising:a conduit extending along a plane having aninlet/outlet opening at each end and adapted to receive a fluid movingin either direction; at least one detecting element disposed within theconduit and movable in the direction of a fluid flow, the detectingelement comprising a lightweight sphere having a smooth exterior surfacein direct contact with the fluid and in substantially continual contactwith the conduit and movable in the direction of fluid flow so that saiddetecting element provides an indication as to which said direction saidfluid is flowing.
 2. An apparatus as set forth in claim 1, having meanscomprising an alarm adapted to be set off by a particular location ofsaid detecting element.
 3. An apparatus as set forth in claim, whereinsaid conduit is at least in part transparent for visual location of saiddetecting element when said detecting element is at at least one of saidinlet/outlet openings.
 4. An apparatus as set forth in claim 3, whereinsaid at least one detecting element includes two detecting elements anda barrier for separating said detecting elements.
 5. An apparatus as setforth in claim 3, wherein said conduit is concave along its length. 6.An apparatus as set forth in claim 3, wherein said conduit lies in ahorizontal plane.
 7. An apparatus as set forth in claim 3, furtherincluding end caps secured to each inlet/outlet opening, said end capshaving an apperature arranged and construed to receive said detectingelement.
 8. An apparatus for detecting pressure differential in adjacentrooms comprising:conduit means connecting said rooms for passage of afluid therebetween when there is a pressure differential between saidrooms; a detecting element positioned in said conduit means for movementin response to the flow of said fluid in response to said pressuredifferential; and a plurality of spaced sensors, each adapted to sensesaid detecting element when said detecting element has moved topreselected positions.
 9. A pressure detecting apparatus as set forth inclaim 8 wherein said, conduit means lies on a horizontal plane.
 10. Apressure detecting apparatus as set forth in claim 8 further comprisingcircuit means, coupled to said spaced sensors, for indicating thepressure differential between said adjacent rooms.
 11. A pressuredetecting apparatus as set forth in claim 8 wherein said rooms arehospital rooms.
 12. A detecting apparatus as set forth in claim 9wherein said detecting element comprises a ball being sufficiently lightto move longitudinally in said conduit in response to the flow of fluidtherethrough.